Leads implanted in or about the heart have been used to reverse certain life threatening arrhythmias, or to stimulate contraction of the heart. Electrical energy is applied to the heart via the leads to return the heart to normal rhythm. Leads have also been used to sense in the atrium or ventricle of the heart and to deliver pacing pulses to the atrium or ventricle.
Cardiac pacing may be performed by the transvenous method or by leads implanted directly onto the epicardium. Permanent transvenous pacing is performed using a lead positioned within one or more chambers of the heart. One or more leads may be positioned in the ventricle or in the atrium through a subclavian vein, and the lead terminal pins are attached to a pacemaker which is implanted subcutaneously.
The lead includes a conductor, such as a coiled conductor, to conduct energy from the pacemaker to the heart, and also signals received from the heart. The lead further includes outer insulation to insulate the conductor. Currently, providing the lead with insulation is done by stringing silicone tubing over the lead. Stringing involves the use of chemicals which swell the silicone tubing, so that the coiled conductor can be pulled through the tubing. As the chemicals evaporate, the tubing contracts around the conductor. Stringing is a complicated manufacturing process which also can result in axial gaps between the conductor and the insulative tubing. The gaps contribute to the outer diameter of the lead.
Accordingly, there is a need for a lead which allows for a less complex manufacturing process and improved insulation. What is also needed is a lead having a smaller outer diameter.